Horizontal synchronizing signal separation circuit

Abstract

In a horizontal synchronizing signal separation circuit, from a composite synchronizing signal which includes a horizontal synchronizing signal and a vertical synchronizing signal, a detection signal indicative of detection of a rising edge of the composite synchronizing signal is generated. A gate is provided through which the detection signal is passed in accordance with a control signal. The control signal is a pulse signal having a predetermined pulse width, which is generated by a circuit to which the output of the gate is input. The output of the gate is also supplied to another circuit which generates a separated horizontal synchronizing signal.

What is claimed is: 
     
       1. A horizontal synchronizing signal separation circuit comprising: detection means, receiving a composite synchronizing signal which includes a horizontal synchronizing signal and a vertical synchronizing signal, for generating and outputting a detection signal of a predetermined width which is indicative of rising edges of the composite synchronizing signal;   gate means, coupled to said detection means, for passing the detection signal in accordance with a control signal;   control signal generation means, coupled to said gate means, for generating a pulse signal in accordance with an output of said gate means, rising edges of the pulse signal being delayed behind the rising edges of the composite synchronizing signal by at least the predetermined width, the pulse signal having a predetermined pulse width and being supplied toward said gate means in order to provide the control signal; and   pulse signal generation means, coupled to said gate means, for generating a further pulse signal with rising edges substantially synchronized with the detection signal which passes through said gate means, the further pulse signal being output as a separated horizontal synchronizing signal.   
     
     
       2. The horizontal synchronizing signal separation circuit according to claim 1, wherein the predetermined pulse width is longer than a half of one horizontal scanning period and shorter than one horizontal scanning period. 
     
     
       3. The horizontal synchronizing signal separation circuit according to claim 1, wherein said control signal generation means comprises a monostable multivibrator. 
     
     
       4. The horizontal synchronizing signal separation circuit according to claim 3, wherein said control signal generation means further comprises an inverter which is connected to an output of said monostable multivibrator, an output of said inverter being output as the control signal. 
     
     
       5. The horizontal synchronizing signal separation circuit according to claim 1, wherein said pulse signal generation means comprises a monostable multivibrator. 
     
     
       6. The horizontal synchronizing signal separation circuit according to claim 3, wherein said control signal generation means further comprises a capacitor and a resistor, both of which are connected to said monostable multivibrator, the predetermined pulse width being controlled by varying a capacitance of said capacitor and a resistance of said resistor. 
     
     
       7. The horizontal synchronizing signal separation circuit according to claim 1, wherein the composite synchronizing signal additionally includes a spurious synchronizing signal, the predetermined pulse width including a period during which pulses of the spurious synchronizing signal exists. 
     
     
       8. A method of separating a horizontal synchronizing signal from a composite synchronizing signal which includes the horizontal synchronizing signal and a vertical synchronizing signal, the method comprising the steps of: generating a detection signal of predetermined width indicative of rising edges of the composite synchronizing signal;   passing the detection signal through gate means in accordance with a control signal;   generating a pulse signal in accordance with the detection signal passed through the gate means, rising edges of the pulse signal being delayed behind the rising edges of the composite synchronizing signal by at least the predetermined width, the pulse signal having a predetermined pulse width and being supplied to the gate means as the control signal; and   generating a further pulse signal with rising edges substantially synchronized with the detection signal which passes through the gate means, the further pulse signal being output as a separated horizontal synchronizing signal.   
     
     
       9. The method of separating a horizontal synchronizing signal according to claim 8, wherein the predetermined pulse width is longer than a half of one horizontal scanning period and shorter than one horizontal scanning period. 
     
     
       10. The method of separating a horizontal synchronizing signal according to claim 8, wherein said step of generating a pulse signal comprises a step of inputting the detection signal passed through the gate means into monostable multivibrator means to generate the pulse signal, the method further comprising a step of inverting the pulse signal to generate the control signal.   
     
     
       11. The horizontal synchronizing signal separation circuit according to claim 1, further comprising inverting means, the pulse signal being inverted by said inverting means, the inverted pulse signal being supplied to said gate means as the control signal.